Saying there are "two types of helm" is a oversimplifying a bit, don't you think?  Since you know your mace/flail distinction, can you explain the difference between a bascinet, a barbute and a sallet?  Anyway, I don't picture Tolkien's warriors ever wearing great helms, as in our history it's a 12 c. invention, and I always picture ME as earlier than that, with simple cap helms like the types worn by vikings, saxons, normans, etc.  (That is my personal view, but I think it fits in with what Tolkien seems to write.  He's really not very interested in those details, though.  I was disappointed to see the big shiny breastplates on Gondorian soldiers in the films, but really like the arms of the Rohirrim.) 
 
Back on topic, I never thought Boromir had a helm, but if one went down the river with him, then I suppose he did.  However, I am convinced that Gimli did not travel with a helm, but only a suit of mail--it's odd that in the film they had it the other way round.  As for Aragorn, I'm sure he would have had a knife--maybe Tolkien didn't count it as a weapon, though.  Perhaps he was emphasizing that he carried no bow?
		 
		
		
		
		
		
		
			
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